Process for a isotactic/syndiotactic polymer blend in a single reactor

ABSTRACT

The present invention is a process for producing a catalyst system to produce polymer blends in a single reactor, polymer blends of isotactic polyolefins and syndiotactic polyolefins. The catalyst system is a combination of at least one metallocene catalyst and at least one conventional supported Ziegler-Natta catalyst. The multi-catalyst system is obtained by mixing the components of at least one metallocene catalyst and at least one conventional supported Ziegler-Natta catalyst. The metallocene catalyst comprises a metallocene compound and an ionizing agent. The conventional supported Ziegler-Natta catalyst comprises an aluminum alkyl and a transition metal compound with, optionally, an electron donor.

This is a Divisional application of co-pending application Ser. No.08/054,916, filed on Apr. 28, 1993.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a process for producing polymer blends from asingle reactor, specifically a process for producing polymer blends ofisotactic polyolefins and syndiotactic polyolefins using a catalystsystem which is a combination of at least one metallocene catalyst andat least one conventional supported Ziegler-Natta catalyst.

2. Description of the Prior Art

It is known that two or more homogeneous catalysts, such as those basedon metallocene compounds, may be combined to effect properties, such asmolecular weight distribution. U.S. Pat. No. 4,530,914 discloses use ofa catalyst system comprising two or more metallocenes in thepolymerization of α-olefins, primarily ethylene, to obtain a broadmolecular weight distribution. The metallocenes each have differentpropagation and termination rate constants. The metallocenes are mixedwith an alumoxane to form the catalyst system.

It is also known that metallocenes may be affixed to a support tosimulate a heterogeneous catalyst. In U.S. Pat. No. 4,808,561 disclosesreacting a metallocene with an alumoxane and forming a reaction productin the presence of a support. The support is a porous material liketalc, inorganic oxides such as Group IIA, IIIA IVA OR IVB metal oxideslike silica, alumina, silica-alumina, magnesia, titania, zirconia andmixtures thereof, and resinous material such as polyolefins like finelydivided polyethylene. The metallocenes and alumoxanes are deposited onthe dehydrated support material.

In U.S. Pat. No. 4,701,432 a support is treated with at least onemetallocene and at least one non-metallocene transition metal compound.To form a catalyst system a cocatalyst comprising an alumoxane and anorganometallic compound of Group IA, IIA, IIB and IIIA is added to thesupported metallocene/non-metallocene. The support is a porous solidsuch as talc or inorganic oxides or resinous materials, preferably aninorganic oxide, such as silica, alumina, silica-alumina, magnesia,titania or zirconia, in finely divided form. By depositing the solublemetallocene on the support material it is converted to a heterogeneoussupported catalyst. The transition metal compound, such as TiCl₄, iscontacted with the support material prior to, after, simultaneously withor separately from contacting the metallocene with the support.

An advantage of a homogeneous metallocene catalyst system is the veryhigh activity of the catalyst and the narrow molecular weightdistribution of the polymer produced with a metallocene catalyst system.The metallocene catalysts suffer from a disadvantage in that the ratioof alumoxane cocatalyst to metallocene is high, requiring extensivetreatment of the polymer product to remove the aluminum. Anotherdisadvantage of the homogenous catalyst system is that the polymerproduct has small particle size and low bulk density. Anotherdisadvantage of the homogeneous catalyst system is that the reactorfouls during polymerization.

It would be advantageous to provide a process to produce a polymer blendof isotactic and syndiotactic polyolefins using a catalyst system of acombination of a homogeneous catalyst with a heterogeneous catalyst in asingle reactor.

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily understood by reference to thefollowing detailed description when considered in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of Differential Scanning Calorimetry results fromExample 1.

FIG. 2 is a graph of Gel Permeation Chromatography results from Example2.

FIG. 3 is a graph of Gel Permeation Chromatography results from Example1.

FIG. 4 is a graph of ¹³ C NMR results from Example 1.

SUMMARY OF THE INVENTION

Accordingly, this invention provides a process and a catalyst system toproduce a polymer blend of isotactic polyolefins and syndiotacticpolyolefins in a single reactor.

Also, this invention provides a process and a catalyst system whicheliminates reactor fouling during polymerization.

These and other objects are accomplished by a process comprising:

a) making a catalyst system comprising at least one metallocene catalystand at least one conventional supported Ziegler-Natta catalyst,

(b) introducing said catalyst system into a polymerization reaction zonecontaining a monomer under polymerization conditions, and

(c) withdrawing a polymer product.

DETAILED DESCRIPTION OF THE INVENTION

The present invention utilizes a multi-catalyst system in thepolymerization of any polymer in which separate polymerizations with ahomogeneous catalyst and with a heterogeneous catalyst are possible.Preferably, the multi-catalyst system is useful in the polymerization ofolefins, more preferably, α-olefins, and, most preferably, propylene.This catalyst system is disclosed in U.S. Ser. No. 776,498 filed Oct.11, 1991, hereby incorporated by reference.

The multi-catalyst system of the present invention is obtained by mixingthe components of at least one metallocene catalyst and at least oneconventional supported Ziegler-Natta catalyst. Generally, the componentsof a metallocene catalyst are a metallocene compound and an ionizingagent. Generally, the components of a conventional supportedZiegler-Natta catalyst are an aluminum alkyl and a transition metalcompound with, optionally, an electron donor.

Any of the conventional heterogeneous Ziegler-Natta transition metalcompound catalyst components for producing isotactic polyolefins can beused in the present invention. The compound is preferably of the generalformula MR_(x) ⁺ where M is the metal, R₊ is a halogen or ahydrocarboxyl and x is the valence of the metal. Preferably, M is aGroup IVB, VB or VIB metal, more preferably a Group IVB, and mostpreferably titanium. Preferably, R₊ is chlorine, bromine, an alkoxy or aphenoxy, more preferably chlorine or ethoxy and most preferably,chlorine. Illustrative examples of the transition metal compoundcatalyst components are TiCl₄, TiBr₄, Ti(OC₂ H₅)₃ Cl , Ti(OC₂ H₅)Cl₃,Ti(OC₄ H₉)₃ Cl , Ti(OC₃ H₇)₂ Cl , Ti(OC₆ H₁₃)₂ Cl₂, Ti(OC₂ H₅)₂ Br₂ andTi(OC₁₂ H₂₅)Cl₃. Mixtures of the transition metal compounds may be used.No restriction on the number of transition metal compounds is made aslong as at least one transition metal compound is present.

The transition metal compound is supported on an inert solid which ischemically unreactive with any of the components of the heterogeneous orhomogeneous catalyst. The support is preferably a magnesium compound.Examples of the magnesium compounds which are to be used to provide asupport source for the catalyst component are magnesium halides,dialkoxymagnesiums, alkyoxymagnesium halides, magnesium oxyhalides,dialkylmagnesiums, magnesium oxide, magnesium hydroxide, andcarboxylates of magnesium.

The aluminum alkyl is of the general formula AlR#₃ where R^(#) is analkyl of from 1-8 carbon atoms and R^(#) may be the same or different.Examples of aluminum alkyls are trimethyl aluminum (TMA), triethylaluminum (TEAl) and triisobutyl aluminum (TiBAl). The preferred aluminumalkyl is TEAl.

The electron donor is any one of the electron donors which are effectivewith conventional supported Ziegler-Natta catalysts. Typically, anelectron donor is an organosilicon compound. Examples of electron donorsare cyclohexylmethyldimethyoxysilane (CMDS), diphenyldimethoxy silane(DPMS) and isobutyltrimethoxy silane (IBMS). Other examples of electrondonors are disclosed in U.S. Pat. Nos. 4,218,339; 4,395,360; 4,328,122;4,473,660; 4,562,173 and 4,547,552, which are hereby incorporated byreference.

The metallocene catalyst is formed from a neutral metallocene compound,i.e., a metal derivative of a cyclopentadiene. The metallocene compounduseful in the present invention contains two cyclopentadiene rings andis of the general formula:

    R"(C.sub.5 H.sub.4)(C.sub.4 H.sub.4-m R'.sub.m C.sub.5 C.sub.4 H.sub.4-n R'.sub.n)MeQ.sub.p

wherein (C₅ H₄) is a cyclopentadienyl ring and (C₄ H_(4-m) R'_(m) C₅ C₄H_(4-n) R'_(n)) is a substituted cyclopentadienyl ring preferably, afluorenyl ring or a substituted fluorenyl ring, the substituentpreferably being alkyl, alkoxy, dialkylamino, halogens, cycloalkyl oraryl; R' is a hydrocarbyl radical, halogen, an alkoxy, an alkoxy alkylor an alkylamino radical having from 1-20 carbon atoms, each R' may bethe same or different; R" is a structural bridge between the (C₅ H₄) and(C₄ H_(4-m) R'_(m) C₅ C₄ H_(4-n) R'_(n)) rings to impart stereorigidityand, preferably, is an alkylene radical having 1-4 carbon atoms, orarylaklyl or diaryl alkyl radical contains 7-20 atoms, a siliconhydrocarbyl compound, a germanium hydrocarbyl compound, an alkylphosphine, or an alkyl amine; Q is a hydrocarbon radical, such as analkyl, aryl, alkenyl, alkylaryl or arylalkyl radical having 1-20 carbonatoms, or is a halogen; Me is a Group IIIB, IVB, VB, or VIB metal aspositioned in the Periodic Table of Elements; 0≦m≦4; 0≦n≦4; and p is thevalence of Me minus 2.

The cyclopentadienyl rings (C₅ H₄) and (C₄ H_(4-m) R'_(m) C₅ C₄ H_(4-n)R'_(n)) must have bilateral or pseudo-bilateral symmetry. Bilateralsymmetry is defined as the condition in which there is no substituentsor one or more substituents on one side and no substituents or one ormore substituents on the other side in the same relative position suchthat a mirror image is formed from one side to another. Pseudobilateralsymmetry is defined as symmetry such that a mirror image exists from oneside to the other in regard to the existence and position ofsubstituents but the substituents themselves are not identical.

The metallocene catalyst is syndiotactic specific or syndiospecific.Such catalyst are described in U.S. Pat. Nos. 4,895,851; 5,162,278;5,155,080; 5,132,381 and European Patent Application Publication Nos. 0387 609; 0 387 690; 0 387 691; and PCT International Publication No. WO92/1218, all of which are hereby incorporated by reference.

The ionizing agent is an alumoxane, an aluminum alkyl, other Lewis acidor a combination thereof which will ionize a neutral metallocenecompound to form a cationic metallocene catalyst. An examples of anionizing agents useful in the present invention is methyl alumoxane(MAO).

The metallocene catalyst is provided in solid form as a complex of themetallocene catalyst component and MAO. This solid complex is producedby the method disclosed in copending patent application Ser. No.08/055,267, hereby incorporated by reference.

Olefins, especially propylene, may be polymerized to form polyolefins inamorphous (atactic) or crystalline forms. Examples of crystalline formsare isotactic and syndiotactic.

Isotactic polypropylene contains principally repeating units withidentical configurations and only a few erratic, brief inversions in thechain. Isotactic polypropylene may be structurally represented as##STR1## The methyl groups attached to the tertiary carbon atoms ofsuccessive monomeric units on the same side of a hypothetical planethrough the main chain of the polymer, e.g., the methyl groups are allabove or below the plane.

Another way of describing the structure is through the use of NMR.Bovey's NMR nomenclature for an isotactic pentad is . . . mmmm . . .with each "m" representing a "meso" dyad or successive methyl groups onthe same side in the plane. As known in the art, any deviation orinversion in the structure of the chain lowers the degree ofisotacticity and crystallinity of the polymer.

A syndiotactic polymer contains principally units of exactly alternatingstereoisomers and is represented by the structure: ##STR2## The methylgroups attached to the tertiary carbon atoms of successive monomericunits in the chain lie on alternate sides of the plane of the polymer.

In NMR nomenclature, this pentad is described as . . . rrrr . . . inwhich each "r" represents a "racemic" dyad, i.e., successive methylgroups on alternate side of the plane. The percentage of r dyads in thechain determines the degree of syndiotacticity of the polymer.Syndiotactic polymers are crystalline and like the isotactic polymersare insoluble in xylene. This crystallinity distinguishes bothsyndiotactic and isotactic polymers from atactic polymer that is solublein xylene.

A polymer chain showing no regular order of repeating unitconfigurations is an atactic polymer. In commercial applications, acertain percentage of atactic polymer is typically produced with theisotactic form.

The invention having been generally described, the following examplesare given as particular embodiments of the invention and to demonstratethe practice and advantages thereof. It is understood that the examplesare given by way of illustration and are not intended to limit thespecification or the claims to follow in any manner.

Solid Metallocene Catalyst Preparation

Methyl aluminoxane supplied as a 10% solution in toluene (density 0.89)was used as the 6cocatalyst. 40 mg of isopropyl(fluorenyl-cyclopentadienyl)zirconium dichloride, was dissolved in 20.0ml of MAO solution; the solution was stirred and the solvent was removedunder high vacuum at room temperature and traces of the remainingsolvent were removed with slight warming. The flask was taken into avacuum Atmospheres dry box; the solid was removed and pulverized toobtain 1.3 g purple solid. A known amount of the solid was weighed outand suspended in 2-4 ml of mineral oil (Amoco-10 NF), in a Wheatonbottle; shaken thoroughly and injected into a stainless steel sampletransfer cylinder as described in the example. Generally, a small amount(estimated to be about 10%) of the solid remained adhered to the glasswall and could not be transferred. It is also likely that small amountof solid remains adhered to the walls of sample transfer cylinder duringinjection.

EXAMPLE 1

10.0 mg of conventional supported Ziegler-Natta catalyst were placed ina stainless steel bomb with 0.2 mmol of cyclohexylmethyldimethoxysilane(CMDS) and 2.0 mmol of triethylaluminum (TEAl). 184 mg ofisopropyl(fluorenyl) (cyclopentadienyl)zirconium dichloride/MAO solidwere suspended in 4 milliliters of mineral oil. Themetallocene/MAO-mineral oil suspension was placed in the bomb. Hydrogen(approximately 16 mmol) was introduced followed by 1.0 liter ofpropylene into a 2 liter Zipperclave reactor kept at 60° C. Contents ofthe bomb were prepolymerized with 0.3 liter of propylene and for 5seconds at 23° C. and then charged into the reactor. The reactortemperature was maintained at 60° C. Polymerization continued for onehour during which time the reactor was maintained at the polymerizationtemperature. At the end of this time polymerization was terminated byrapidly venting the reactor of unreacted monomer. The polymer yield andanalysis is shown in Table I.

EXAMPLE 2

The procedure of Example 1 was followed except that only themetallocene/MAO of solid (184.0 ml) and TEAl (2.0 mmol) were used in thebomb and hydrogen was omitted. The reactor temperature was initially 20°C. and was increased to 60° C. after the contents of the bomb werecharged to the reactor with 0.3 liter of propylene. The polymer yieldand analysis is shown in Table I.

EXAMPLE 3

The procedure of Example 1 was followed except that the conventionalZiegler-Natta catalyst was not added and the other contents were used inidentical quantities.

                                      TABLE I                                     __________________________________________________________________________                HETEROGENEOUS                         POWDER                          TEA1                                                                              CMDS                                                                              CATALYST   METALLOCENE/MAO                                                                            METALLOCENE                                                                             H.sub.2                                                                           YIELD                       RUN (mmol)                                                                            (mmol)                                                                            (mg)       AMOUNT (mg)  AMOUNT (mg)                                                                             (mmol)                                                                            (g)                         __________________________________________________________________________    1   2.0 0.2 10.0       184          4         15.7                                                                              177                         2   2.0 0.0 0.0        184          4          0.0                                                                              140                         3   2.0 0.2 0.0        184          4         15.7                                                                               28                         __________________________________________________________________________        SOLID  TOLUENE                                                                              TOTAL CATALYST PER CENT                                                                             BULK                                      FOULING                                                                              EXTRACT                                                                              YIELD EFFICIENCY                                                                             FOULING                                                                              DENSITY                                                                             T.sub.m                         RUN (g)    (g)    (g)   (g/g · h)                                                                     (%)    (g/cc)                                                                              (°C.)                                                                       MWD                        __________________________________________________________________________    1   0      0      177   n.d.sup.a)                                                                             0      0.40  159.sup.b)                                                                         13.3.sup.c)                2   0      0      140   35000    0      0.32  135  3.0.sup.d)                 3   0      0       28    7000    0      n.d   n.d                             __________________________________________________________________________     .sup.a) n.d = not determined                                                  .sup.b) Small DSC peaks at 126° C. and 135° C. can be seen      due to the presence of syndiotactic polypropylene                             .sup.c) bimodal distribution; Mw = 441; Mn = 33.0; It is important to not     that MWD of IPP obtained under similar conditions in the presence of          conventional ZieglerNatta cataylst system is approximately 8.0.               .sup.d) Mw = 57.4 × 10.sup.3 ; M.sub.n = 18.9 × 10.sup.3     

The standard polymer characterization techniques, namely DSC(Differential Scanning Calorimetry) , GPC (Gel PermeationChromatography) and carbon 13 nuclear magnetic resonance (¹³ C NMR)spectroscopy, strongly suggest that the polymer obtained with the mixedcatalyst is indeed a blend of syndiotactic and isotactic polypropylene.For example, DSC shows (FIG. 1) the presence of two small peaks atapproximately 125° C. and 135° C. corresponding to the melting peaks ofsyndiotactic polymer obtained with the metallocene and MAO solid. It isalso obvious from DSC that isotactic polypropylene is the majorcomponent of the blend. GPC teaches that the molecular weightdistribution of the polymer is much broader than those obtained when theconventional Ziegler-Natta or metallocene and alumoxane systemsseparately under the same conditions. Thus for example, thepolydispersity of isotactic polypropylene (iPP) obtained with theconventional Ziegler-Natta catalyst used in the present system isapproximately 8.0, whereas that of the syndiotactic polypropylene (sPP)obtained with solid MAO and metallocene catalyst used is around 3.0(FIG. 2). However, the polydispersity of the iPP/sPP blend obtained withthe mixed catalyst system is 13 (FIG. 3). ¹³ C NMR (FIG. 4) of thepolymer provides the most conclusive evidence for the presence of twotypes of stereoregular polypropylene in the product blend. The mmmm:rrrratio for the polymer blend product was 77:13 which suggest presence ofsubstantial amounts (>10%) of syndiotactic PP in the predominantlyisotactic polymer sample. Generally the isotactic polypropylene polymerobtained with the conventional Ziegler-Natta catalyst contains onlytraces (<0.5%) of syndiotactic component.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

What is claimed as new and desired to be secured by Letter of Patent of the United States is:
 1. A method of making a catalyst system comprising:a) mixing the following components to form a syndiospecific metallocene catalyst consisting of:1) a neutral metallocene compound of the general formula

    R"(C.sub.5 H.sub.4)(C.sub.4 H.sub.4-m R'.sub.m C.sub.5 C.sub.4 H.sub.4-n R'.sub.n)MeQ.sub.p

wherein (C₅ H₄) is a cyclopentadienyl ring and (C₄ H_(4-m) R'_(m) C₅ C₄ H_(4-n) R'_(n)) is a substituted cyclopentadienyl ring wherein (C₅ H₄) and (C₄ H_(4-m) R'_(m) C₅ C₄ H_(4-n) R'_(n)) have bilateral or pseudo-bilateral symmetry; R' is a hydrocarbyl radical having from 1-20 carbon atoms, a halogen, an alkoxy, an alkoxy alkyl or an alkylamino radical, each R' may be the same or different; R" is a structural bridge between the (C₅ H₄) and (C₄ H_(4-m) R'_(m) C₅ C₄ H_(4-n) R'_(n)) rings to impart stereorigidity; Q is a hydrocarbon radical or is a halogen; Me is a Group IVB metal as positioned in the Periodic Table of Elements; 0≦m≦4; 0≦n≦4; and p is the valence of Me minus 2; and 2) an aluminoxane in solvent, b) extracting solvent to form a solid complex consisting of the metallocene and the aluminoxane, c) suspending the solid in mineral oil, d) separately mixing:1) a conventional supported Ziegler-Natta catalyst component comprising a transition metal compound of the general formula MR*_(x) where M is titanium, R* is a halogen or a hydrocarboxyl and x is the valence of the metal and 2) an aluminum alkyl of the general formula AlR¹⁹⁰ ₃ where R^(#) is an alkyl of from 1-8 carbon atoms and R^(#) may be the same or different, to form a conventional supported Ziegler-Natta catalyst, 3) an electron donor organosilicon compound, e) mixing the metallocene catalyst in mineral oil and the conventional supported Ziegler-Natta catalyst.
 2. A method as recited in claim 1 wherein R" is a hydrocarbyl radical selected from the group consisting of an alkylene radical having one to four carbon atoms, a dialkyl germanium, a dialkyl silicon, an alkyl phosphine and an amine radical, M is a Group IVB metal, R' is a halogen or alkyl.
 3. A method as recited in claim 1 wherein R" is an isopropenyl radical.
 4. A method as recited in claim 1 wherein the aluminoxane is methyl alumoxane.
 5. A method as recited in claim 1 wherein R* is chlorine, bromine, an alkoxy or a phenoxy.
 6. A method as recited in claim 1 wherein R* is chlorine or ethoxy.
 7. A method as recited in claim 1 wherein the transition metal compound is selected from the group consisting of TiCl₄, TiBr₄, Ti(OC₂ H₅)₃ Cl, Ti(OC₂ H₅)Cl₃, Ti(OC₄ H₉)₃ Cl, Ti(OC₃ H₇)₂ Cl₂, Ti(OC₆ H₁₃)₂ Cl₂, Ti(OC₂ H₅)₂ Br₂ and Ti(OC₁₂ H₂₅)Cl₃.
 8. A method as recited in claim 1 wherein the aluminum alkyl is selected from the group consisting of trimethyl aluminum, triethyl aluminum and triisobutyl aluminum.
 9. A method as recited in claim 1 wherein the electron donor is selected from the group consisting of cyclohexylmethyl dimethyoxysilane, diphenyldimethoxysilane and isobutyltrimethoxy silane. 